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+*******************************
+HOWTO Use Python in the web
+*******************************
+:Author: Marek Kubica
+.. topic:: Abstract
+This document shows how Python fits into the web.  It presents some ways on
+how to integrate Python with the web server and general practices useful for
+developing web sites.
+Programming for the Web has become a hot topic since the raise of the "Web 2.0",
+which focuses on user-generated content on web sites.  It has always been
+possible to use Python for creating web sites, but it was a rather tedious task.
+Therefore, many so-called "frameworks" and helper tools were created to help
+developers creating sites faster and these sites being more robust.  This HOWTO
+describes some of the methods used to combine Python with a web server to create
+dynamic content.  It is not meant as a general introduction as this topic is far
+too broad to be covered in one single document.  However, a short overview of
+the most popular libraries is provided.
+.. seealso::
+While this HOWTO tries to give an overview over Python in the Web, it cannot
+always be as up to date as desired.  Web development in Python is moving
+forward rapidly, so the wiki page on `Web Programming
+<http://wiki.python.org/moin/WebProgramming>`_ might be more in sync with
+recent development.
+The low-level view
+==================
+.. .. image:: http.png
+When a user enters a web site, his browser makes a connection to the site's
+webserver (this is called the *request*).  The server looks up the file in the
+file system and sends it back to the user's browser, which displays it (this is
+the *response*).  This is roughly how the unterlying protocol, HTTP works.
+Now, dynamic web sites are not files in the file system, but rather programs
+which are run by the web server when a request comes in.  They can do all sorts
+of useful things, like display the postings of a bulletin board, show your
+mails, configurate software or just display the current time.  These programs
+can be written in about any programming language the server supports, so it is
+easy to use Python for creating dynamic web sites.
+As most of HTTP servers are written in C or C++, they cannot execute Python code
+in a simple way -- a bridge is needed between the server and the program.  These
+bridges or rather interfaces define how programs interact with the server.  In
+the past there have been numerous attempts to create the best possible
+interface, but there are only a few worth mentioning.
+Not every web server supports every interface.  Many web servers do support only
+old, now-obsolete interfaces.  But they can often be extended using some
+third-party modules to support new interfaces.
+Common Gateway Interface
+------------------------
+This interface is the oldest one, supported by nearly every web server out of
+the box.  Programs using CGI to communicate with their web server need to be
+started by the server for every request.  So, every request starts a new Python
+interpreter -- which takes some time to start up -- thus making the whole
+interface only usable for low load situations.
+The upside of CGI is that it is simple -- writing a program which uses CGI is a
+matter of about three lines of code.  But this simplicity comes at a price: it
+does very few things to help the developer.
+Writing CGI programs, while still possible, is not recommended anymore.  With
+WSGI (more on that later) it is possible to write programs that emulate CGI, so
+they can be run as CGI if no better option is available.
+.. seealso::
+The Python standard library includes some modules that are helpful for
+creating plain CGI programs:
+* :mod:`cgi` -- Handling of user input in CGI scripts
+* :mod:`cgitb` -- Displays nice tracebacks when errors happen in of CGI
+applications, instead of presenting a "500 Internal Server Error" message
+The Python wiki features a page on `CGI scripts
+<http://wiki.python.org/moin/CgiScripts>`_ with some additional information
+about CGI in Python.
+Simple script for testing CGI
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+To test whether your web server works with CGI, you can use this short and
+simple CGI program::
+#!/usr/bin/env python
+# -*- coding: UTF-8 -*-
+# enable debugging
+import cgitb; cgitb.enable()
+print "Content-Type: text/plain;charset=utf-8"
+print
+print "Hello World!"
+You need to write this code into a file with a ``.py`` or ``.cgi`` extension,
+this depends on your web server configuration.  Depending on your web server
+configuration, this file may also need to be in a ``cgi-bin`` folder, for
+security reasons.
+You might wonder what the ``cgitb`` line is about.  This line makes it possible
+to display a nice traceback instead of just crashing and displaying an "Internal
+Server Error" in the user's browser.  This is useful for debugging, but it might
+risk exposing some confident data to the user.  Don't use it when the script is
+ready for production use.  Still, you should *always* catch exceptions, and
+display proper error pages -- end-users don't like to see nondescript "Internal
+Server Errors" in their browsers.
+Setting up CGI on your own server
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+If you don't have your own web server, this does not apply to you.  You can
+check whether if works as-is and if not you need to talk to the administrator of
+your web server anyway. If it is a big hoster, you can try filing a ticket
+asking for Python support.
+If you're your own administrator or want to install it for testing purposes on
+your own computers, you have to configure it by yourself.  There is no one and
+single way on how to configure CGI, as there are many web servers with different
+configuration options.  The currently most widely used free web server is
+`Apache HTTPd <http://httpd.apache.org/>`_, Apache for short -- this is the one
+that most people use, it can be easily installed on nearly every system using
+the systems' package management.  But `lighttpd <http://www.lighttpd.net>`_ has
+been gaining attention since some time and is said to have a better performance.
+On many systems this server can also be installed using the package management,
+so manually compiling the web server is never needed.
+* On Apache you can take a look into the `Dynamic Content with CGI
+<http://httpd.apache.org/docs/2.2/howto/cgi.html>`_ tutorial, where everything
+is described.  Most of the time it is enough just to set ``+ExecCGI``.  The
+tutorial also describes the most common gotchas that might arise.
+* On lighttpd you need to use the `CGI module
+<http://trac.lighttpd.net/trac/wiki/Docs%3AModCGI>`_ which can be configured
+in a straightforward way.  It boils down to setting ``cgi.assign`` properly.
+Common problems with CGI scripts
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Trying to use CGI sometimes leads to small annoyances that one might experience
+while trying to get these scripts to run.  Sometimes it happens that a seemingly
+correct script does not work as expected, which is caused by some small hidden
+reason that's difficult to spot.
+Some of these reasons are:
+* The Python script is not marked executable.  When CGI scripts are not
+executable most of the web servers will let the user download it, instead of
+running it and sending the output to the user.  For CGI scripts to run
+properly the ``+x`` bit needs to be set.  Using ``chmod a+x your_script.py``
+might already solve the problem.
+* The line endings must be of Unix-type.  This is important because the web
+server checks the first line of the script (called shebang) and tries to run
+the program specified there.  It gets easily confused by Windows line endings
+(Carriage Return & Line Feed, also called CRLF), so you have to convert the
+file to Unix line endings (only Line Feed, LF).  This can be done
+automatically by uploading the file via FTP in text mode instead of binary
+mode, but the preferred way is just telling your editor to save the files with
+Unix line endings.  Most proper editors support this.
+* Your web server must be able to read the file, you need to make sure the
+permissions are fine.  Often the server runs as user and group ``www-data``,
+so it might be worth a try to change the file ownership or making the file
+world readable by using ``chmod a+r your_script.py``.
+* The webserver must be able to know that the file you're trying to access is a
+CGI script.  Check the configuration of your web server, maybe there is some
+mistake.
+* The path to the interpreter in the shebang (``#!/usr/bin/env python``) must be
+currect.  This line calls ``/usr/bin/env`` to find Python, but it'll fail if
+there is no ``/usr/bin/env``.  If you know where your Python is installed, you
+can also use that path.  The commands ``whereis python`` and ``type -p
+python`` might also help to find where it is installed.  Once this is known,
+the shebang line can be changed accordingly: ``#!/usr/bin/python``.
+* The file must not contain a BOM (Byte Order Mark). The BOM is meant for
+determining the byte order of UTF-16 encodings, but some editors write this
+also into UTF-8 files.  The BOM interferes with the shebang line, so be sure
+to tell your editor not to write the BOM.
+* :ref:`mod-python` might be making problems.  mod_python is able to handle CGI
+scripts by itself, but it can also be a source for problems.  Be sure you
+disable it.
+.. _mod-python:
+mod_python
+----------
+People coming from PHP often find it hard to grasp how to use Python in the web.
+Their first thought is mostly `mod_python <http://www.modpython.org/>`_ because
+they think that this is the equivalent to ``mod_php``.  Actually it is not
+really.  It does embed the interpreter into the Apache process, thus speeding up
+requests by not having to start a Python interpreter every request.  On the
+other hand, it is by far not "Python intermixed with HTML" as PHP often does.
+The Python equivalent of that is a template engine.  mod_python itself is much
+more powerful and gives more access to Apache internals.  It can emulate CGI, it
+can work an a "Python Server Pages" mode similar to JSP which is "HTML
+intermangled with Python" and it has a "Publisher" which destignates one file to
+accept all requests and decide on what to do then.
+But mod_python has some problems.  Unlike the PHP interpreter the Python
+interpreter uses caching when executing files, so when changing a file the whole
+web server needs to be re-started to update.  Another problem ist the basic
+concept -- Apache starts some child processes to handle the requests and
+unfortunately every child process needs to load the whole Python interpreter
+even if it does not use it.  This makes the whole web server slower.  Another
+problem is that as mod_python is linked against a specific version of
+``libpython``, it is not possible to switch from an older version to a newer
+(e.g. 2.4 to 2.5) without recompiling mod_python.  mod_python is also bound to
+the Apache web server, so programs written for mod_python cannot easily run on
+other web servers.
+These are the reasons why mod_python should be avoided when writing new
+programs.  In some circumstances it might be still a good idea to use mod_python
+for deployment, but WSGI makes it possible to run WSGI programs under mod_python
+as well.
+FastCGI and SCGI
+----------------
+FastCGI and SCGI try to solve the performance problem of CGI in another way.
+Instead of embedding the interpreter into the web server, they create
+long-running processes which run in the background. There still is some module
+in the web server which makes it possible for the web server to "speak" with the
+background process.  As the background process is independent from the server,
+it can be written in any language of course also in Python.  The language just
+needs to have a library which handles the communication with the web server.
+The difference between FastCGI and SCGI is very small, as SCGI is essentially
+just a "simpler FastCGI".  But as the web server support for SCGI is limited
+most people use FastCGI instead, which works the same way.  Almost everything
+that applies to SCGI also applies to FastCGI as well, so we'll only write about
+the latter.
+These days, FastCGI is never used directly.  Just like ``mod_python`` it is only
+used for the deployment of WSGI applications.
+.. seealso::
+* `FastCGI, SCGI, and Apache: Background and Future
+<http://www.vmunix.com/mark/blog/archives/2006/01/02/fastcgi-scgi-and-apache-background-and-future/>`_
+is a discussion on why the concept of FastCGI and SCGI is better that that
+of mod_python.
+Setting up FastCGI
+^^^^^^^^^^^^^^^^^^
+Depending on the web server you need to have a special module.
+* Apache has both `mod_fastcgi <http://www.fastcgi.com/>`_ and `mod_fcgid
+<http://fastcgi.coremail.cn/>`_.  ``mod_fastcgi`` is the original one, but it
+has some licensing issues that's why it is sometimes considered non-free.
+``mod_fcgid`` is a smaller, compatible alternative. One of these modules needs
+to be loaded by Apache.
+* lighttpd ships its own `FastCGI module
+<http://trac.lighttpd.net/trac/wiki/Docs%3AModFastCGI>`_ as well as an `SCGI
+module <http://trac.lighttpd.net/trac/wiki/Docs%3AModSCGI>`_.
+* nginx also supports `FastCGI
+<http://wiki.codemongers.com/NginxSimplePythonFCGI>`_.
+Once you have installed and configured the module, you can test it with the
+following WSGI-application::
+#!/usr/bin/env python
+# -*- coding: UTF-8 -*-
+from cgi import escape
+import sys, os
+from flup.server.fcgi import WSGIServer
+def app(environ, start_response):
+start_response('200 OK', [('Content-Type', 'text/html')])
+yield '<h1>FastCGI Environment</h1>'
+yield '<table>'
+for k, v in sorted(environ.items()):
+yield '<tr><th>%s</th><td>%s</td></tr>' % (escape(k), escape(v))
+yield '</table>'
+WSGIServer(app).run()
+This is a simple WSGI application, but you need to install `flup
+<http://pypi.python.org/pypi/flup/1.0>`_ first, as flup handles the low level
+FastCGI access.
+.. seealso::
+There is some documentation on `setting up Django with FastCGI
+<http://www.djangoproject.com/documentation/fastcgi/>`_, most of which can be
+reused for other WSGI-compliant frameworks and libraries.  Only the
+``manage.py`` part has to be changed, the example used here can be used
+instead. Django does more or less the exact same thing.
+mod_wsgi
+--------
+`mod_wsgi <http://www.modwsgi.org/>`_ is an attempt to get rid of the low level
+gateways.  As FastCGI, SCGI, mod_python are mostly used to deploy WSGI
+applications anyway, mod_wsgi was started to directly embed WSGI aplications
+into the Apache web server.  The benefit from this approach is that WSGI
+applications can be deployed much easier as is is specially designed to host
+WSGI applications -- unlike the other low level methods which have glue code to
+host WSGI applications (like flup which was mentioned before).  The downside is
+that mod_wsgi is limited to the Apache web server, other servers would need
+their own implementations of mod_wsgi.
+It supports two modes: the embedded mode in which it integrates with the Apache
+process and the daemon mode which is more FastCGI-like.  Contrary to FastCGI,
+mod_wsgi handles the worker-processes by itself which makes administration
+easier.
+.. _WSGI:
+Step back: WSGI
+===============
+WSGI was already mentioned several times so it has to be something important.
+In fact it really is, so now it's time to explain.
+The *Web Server Gateway Interface*, :pep:`333` or WSGI for short is currently
+the best possible way to Python web programming.  While it is great for
+programmers writing frameworks, the normal person does not need to get in direct
+contact with it.  But when choosing a framework for web development it is a good
+idea to take one which supports WSGI.
+The big profit from WSGI is the unification.  When your program is compatible
+with WSGI -- that means that your framework has support for WSGI, your program
+can be deployed on every web server interface for which there are WSGI wrappers.
+So you do not need to care about whether the user uses mod_python or FastCGI --
+with WSGI it just works on any gateway interface.  The Python standard library
+contains its own WSGI server :mod:`wsgiref`, which is a small web server that
+can be used for testing.
+A really great WSGI feature are the middlewares.  Middlewares are layers around
+your program which can add various functionality to it.  There is a `number of
+middlewares <http://wsgi.org/wsgi/Middleware_and_Utilities>`_ already available.
+For example, instead of writing your own session management (to identify a user
+in subsequent requests, as HTTP does not maintain state, so it does now know
+that the requests belong to the same user) you can just take one middleware,
+plug it in and you can rely an already existing functionality.  The same thing
+is compression -- say you want to compress your HTML using gzip, to save your
+server's bandwidth.  So you only need to plug-in a middleware and you're done.
+Authentication is also a problem easily solved using a middleware.
+So, generally -- although WSGI may seem complex, the initial phase of learning
+can be very rewarding as WSGI does already have solutions to many problems that
+might arise while writing web sites.
+WSGI Servers
+------------
+The code that is used to connect to various low level gateways like CGI or
+mod_python is called *WSGI server*.  One of these servers is ``flup`` which was
+already mentioned and supports FastCGI, SCGI as well as `AJP
+<http://en.wikipedia.org/wiki/Apache_JServ_Protocol>`_.  Some of these servers
+are written in Python as ``flup`` is, but there also exist others which are
+written in C and can be used as drop-in replacements.
+There are quite a lot of servers already available, so a Python web application
+can be deployed nearly everywhere.  This is one big advantage that Python has
+compared with other web techniques.
+.. seealso::
+A good overview of all WSGI-related code can be found in the `WSGI wiki
+<http://wsgi.org/wsgi>`_, which contains an extensive list of `WSGI servers
+<http://wsgi.org/wsgi/Servers>`_, which can be used by *every* application
+supporting WSGI.
+You might be interested in some WSGI-supporting modules already contained in
+the standard library, namely:
+* :mod:`wsgiref` -- some tiny utilities and servers for WSGI
+Case study: MoinMoin
+--------------------
+What does WSGI give the web application developer?  Let's take a look on one
+long existing web application written in Python without using WSGI.
+One of the most widely used wiki software is `MoinMoin <http://moinmo.in/>`_.
+It was created in 2000, so it predates WSGI by about three years.  While it now
+includes support for WSGI, older versions needed separate code to run on CGI,
+mod_python, FastCGI and standalone.  Now, this all is possible by using WSGI and
+the already-written gateways.  For running with on FastCGI ``flup`` can be used,
+for running a standalone server :mod:`wsgiref` is the way to go.
+Model-view-controller
+=====================
+The term *MVC* is often heard in statements like "framework *foo* supports MVC".
+While MVC is not really something technical but rather organisational, many web
+frameworks use this model to help the developer to bring structure into his
+program.  Bigger web applications can have lots of code so it is a good idea to
+have structure in the program right from the beginnings.  That way, even users
+of other frameworks (or even languages, as MVC is nothing Python-specific) can
+understand the existing code easier, as they are already familiar with the
+structure.
+MVC stands for three components:
+* The *model*.  This is the data that is meant to modify.  In Python frameworks
+this component is often represented by the classes used by the
+object-relational mapper.  So, all declarations go here.
+* The *view*.  This component's job is to display the data of the model to the
+user.  Typically this component is represented by the templates.
+* The *controller*.  This is the layer between the user and the model.  The
+controller reacts on user actions (like opening some specific URL) and tells
+the model to modify the data if neccessary.
+While one might think that MVC is a complex design pattern, in fact it is not.
+It is used in Python because it has turned out to be useful for creating clean,
+maintainable web sites.
+.. note::
+While not all Python frameworks explicitly support MVC, it is often trivial
+to create a web site which uses the MVC pattern by seperating the data logic
+(the model) from the user interaction logic (the controller) and the
+templates (the view).  That's why it is important not to write unneccessary
+Python code in the templates -- it is against MVC and creates more chaos.
+.. seealso::
+The english Wikipedia has an article about the `Model-View-Controller pattern
+<http://en.wikipedia.org/wiki/Model-view-controller>`_, which includes a long
+list of web frameworks for different programming languages.
+Ingredients for web sites
+=========================
+Web sites are complex constructs, so tools were created to help the web site
+developer to make his work maintainable.  None of these tools are in any way
+Python specific, they also exist for other programming languages as well.  Of
+course, developers are not forced to use these tools and often there is no
+"best" tool, but it is worth informing yourself before choosing something
+because of the big number of helpers that the developer can use.
+.. seealso::
+People have written far more components that can be combined than these
+presented here.  The Python wiki has a page about these components, called
+`Web Components <http://wiki.python.org/moin/WebComponents>`_.
+Templates
+---------
+Mixing of HTML and Python code is possible with some libraries.  While
+convenient at first, it leads to horribly unmaintainable code.  That's why
+templates exist.  Templates are, in the simplest case, just HTML files with
+placeholders.  The HTML is sent to the user's browser after filling out the
+placeholders.
+Python already includes such simple templates::
+# a simple template
+template = "<html><body><h1>Hello %s!</h1></body></html>"
+print template % "Reader"
+The Python standard library also includes some more advanced templates usable
+through :class:`string.Template`, but in HTML templates it is needed to use
+conditional and looping contructs like Python's *for* and *if*.  So, some
+*template engine* is needed.
+Now, Python has a lot of template engines which can be used with or without a
+`framework`_.  Some of these are using a plain-text programming language which
+is very easy to learn as it is quite limited while others use XML so the
+template output is always guaranteed to be valid XML.  Some `frameworks`_ ship
+their own template engine or recommend one particular.  If one is not yet sure,
+using these is a good idea.
+.. note::
+While Python has quite a lot of different template engines it usually does
+not make sense to use a homebrewed template system.  The time needed to
+evaluate all templating systems is not really worth it, better invest the
+time in looking through the most popular ones.  Some frameworks have their
+own template engine or have a recommentation for one.  It's wise to use
+these.
+Popular template engines include:
+* Mako
+* Genshi
+* Jinja
+.. seealso::
+Lots of different template engines divide the attention between themselves
+because it's easy to create them in Python.  The page `Templating
+<http://wiki.python.org/moin/Templating>`_ in the wiki lists a big,
+ever-growing number of these.
+Data persistence
+----------------
+*Data persistence*, while sounding very complicated is just about storing data.
+This data might be the text of blog entries, the postings of a bulletin board or
+the text of a wiki page.  As always, there are different ways to store
+informations on a web server.
+Often relational database engines like `MySQL <http://www.mysql.com/>`_ or
+`PostgreSQL <http://http://www.postgresql.org/>`_ are used due to their good
+performance handling very large databases consisting of up to millions of
+entries.  These are *queried* using a language called `SQL
+<http://en.wikipedia.org/wiki/SQL>`_.  Python programmers in general do not like
+SQL too much, they prefer to work with objects.  It is possible to save Python
+objects into a database using a technology called `ORM
+<http://en.wikipedia.org/wiki/Object-relational_mapping>`_.  ORM translates all
+object-oriented access into SQL code under the hood, the user does not need to
+think about it.  Most `frameworks`_ use ORMs and it works quite well.
+A second possibility is using files that are saved on the hard disk (sometimes
+called flatfiles).  This is very easy, but is not too fast.  There is even a
+small database engine called `SQLite <http://www.sqlite.org/>`_ which is bundled
+with Python in the :mod:`sqlite` module and uses only one file.  This database
+can be used to store objects via an ORM and has no other dependencies.  For
+smaller sites SQLite is just enough.  But it is not the only way in which data
+can be saved into the file systems.  Sometimes normal, plain text files are
+enough.
+The third and least used possibility are so-called object oriented databases.
+These databases store the *actual objects* instead of the relations that
+OR-mapping creates between rows in a database.  This has the advantage that
+nearly all objects can be saven in a straightforward way, unlike in relational
+databases where some objects are very hard to represent with ORMs.
+`Frameworks`_ often give the users hints on which method to choose, it is
+usually a good idea to stick to these unless there are some special requirements
+which require to use the one method and not the other.
+.. seealso::
+* `Persistence Tools <http://wiki.python.org/moin/PersistenceTools>`_ lists
+possibilities on how to save data in the file system, some of these modules
+are part of the standard library
+* `Database Programming <http://wiki.python.org/moin/DatabaseProgramming>`_
+helps on choosing a method on how to save the data
+* `SQLAlchemy <http://www.sqlalchemy.org/>`_, the most powerful OR-Mapper for
+Python and `Elixir <http://elixir.ematia.de/>`_ which makes it easier to
+use
+* `SQLObject <http://www.sqlobject.org/>`_, another popular OR-Mapper
+* `ZODB <https://launchpad.net/zodb>`_ and `Durus
+<http://www.mems-exchange.org/software/durus/>`_, two object oriented
+databases
+.. _framework:
+Frameworks
+==========
+As web sites can easily become quite large, there are so-called frameworks which
+were created to help the developer with making these sites.  Although the most
+well-known framework is Ruby on Rails, Python does also have its own frameworks
+which are partly inspired by Rails or which were existing a long time before
+Rails.
+Two possible approaches to web frameworks exist: the minimalistic approach and
+the all-inclusive approach (somtimes called *full-stack*). Frameworks which are
+all-inclusive give you everything you need to start working, like a template
+engine, some way to save and access data in databases and many features more.
+Most users are best off using these as they are widely used by lots of other
+users and well documented in form of books and tutorials.  Other web frameworks
+go the minimalistic approach trying to be as flexible as possible leaving the
+user the freedom to choose what's best for him.
+The majority of users is best off with all-inclusive framewors.  They bring
+everything along so a user can just jump in and start to code.  While they do
+have some limitations they can fullfill 80% of what one will ever want to
+perfectly.  They consist of various components which are designed to work
+together as good as possible.
+The multitude of web frameworks written in Python demonstrates that it is really
+easy to write one.  One of the most well-known web applications written in
+Python is `Zope <http://www.zope.org/>`_ which can be regarded as some kind of
+big framework.  But Zope was not the only framework, there were some others
+which are by now nearly forgotten.  These do not need to be mentioned anymore,
+because most people that used them moved on to newer ones.
+Some notable frameworks
+-----------------------
+There is an incredible number of frameworks, so there is no way to describe them
+all.  It is not even neccessary, as most of these frameworks are nothing special
+and everything that can be done with these can also be done with one of the
+popular ones.
+Django
+^^^^^^
+`Django <http://www.djangoproject.com/>`_ is a framework consisting of several
+tightly coupled elements which were written from scratch and work together very
+well.  It includes an ORM which is quite powerful while being simple to use and
+has a great online administration interface which makes it possible to edit the
+data in the database with a browser.  The template engine is text-based and is
+designed to be usable for page designers who cannot write Python.  It supports
+so-called template inheritance and filters (which work like Unix pipes).  Django
+has many handy features bundled, like creation of RSS feeds or generic views
+which make it possible to write web sites nearly without any Python code.
+It has a big, international community which has created many sites using Django.
+There are also quite a lot of add-on projects which extend Django's normal
+functionality.  This is partly due to Django's well written `online
+documentation <http://doc.djangoproject.com/>`_ and the `Django book
+<http://www.djangobook.com/>`_.
+.. note::
+Although Django is an MVC-style framework, it calls the components
+differently, which is described in the `Django FAQ
+<http://www.djangoproject.com/documentation/faq/#django-appears-to-be-a-mvc-framework-but-you-call-the-controller-the-view-and-the-view-the-template-how-come-you-don-t-use-the-standard-names>`_.
+TurboGears
+^^^^^^^^^^
+The other popular web framework in Python is `TurboGears
+<http://www.turbogears.org/>`_.  It takes the approach of using already existing
+components and combining them with glue code to create a seamless experience.
+TurboGears gives the user more flexibility on which components to choose, the
+ORM can be switched between some easy to use but limited and complex but very
+powerful.  Same goes for the template engine.  One strong point about TurboGears
+is that the components that it consists of can be used easily in other projects
+without depending on TurboGears, for example the underlying web server CherryPy.
+The documentation can be found in the `TurboGears wiki
+<http://docs.turbogears.org/>`_, where links to screencasts can be found.
+TurboGears has also an active user community which can respond to most related
+questions.  There is also a `TurboGears book <http://turbogearsbook.com/>`_
+published, which is a good starting point.
+The plan for the next major version of TurboGears, version 2.0 is to switch to a
+more flexible base provided by another very flexible web framework called
+`Pylons <http://pylonshq.com/>`_.
+Other notable frameworks
+^^^^^^^^^^^^^^^^^^^^^^^^
+These two are of course not the only frameworks that are available, there are
+also some less-popular frameworks worth mentioning.
+One of these is the already mentioned Zope, which has been around for quite a
+long time.  With Zope 2.x having been known as rather un-pythonic, the newer
+Zope 3.x tries to change that and therefore gets more acceptance from Python
+programmers.  These efforts already showed results, there is a project which
+connects Zope with WSGI called `Repoze <http://repoze.org/>`_ and another
+project called `Grok <http://grok.zope.org/>`_ which makes it possible for
+"normal" Python programmers use the very mature Zope components.
+Another framework that's already been mentioned is `Pylons`_.  Pylons is much
+like TurboGears with ab even stronger emphasis on flexibility, which is bought
+at the cost of being more difficult to use.  Nearly every component can be
+exchanged, which makes it neccessary to use the documentation of every single
+component, because there are so many Pylons combinations possible that can
+satisfy every requirement.  Pylons builds upon `Paste
+<http://pythonpaste.org/>`_, an extensive set of tools which are handy for WSGI.
+And that's still not everything.  The most up-to-date information can always be
+found in the Python wiki.
+.. seealso::
+The Python wiki contains an extensive list of `web frameworks
+<http://wiki.python.org/moin/WebFrameworks>`_.
+Most frameworks also have their own mailing lists and IRC channels, look out
+for these on the projects' websites.  There is also a general "Python in the
+Web" IRC channel on freenode called `#python.web
+<http://wiki.python.org/moin/PoundPythonWeb>`_.